1. Field of the Invention
The present invention relates to electrical and electronic circuits and systems. More specifically, the present invention relates to microwave switches.
2. Description of the Related Art
Microwave switches are used in a wide variety of applications such as communications and active phased array radar systems. For example, switches may be used to control the direction of a radio frequency (RF) or microwave signal or to provide phase and amplitude control functions in a transmit/receive (T/R) module.
Silicon-germanium (SiGe) technology permits the integration of advanced MMICs, low power VLSI digital electronics, and low frequency analog circuits in a single high yield process. The availability of several high performance microwave passive and active devices on the same wafer, including SiGe HBTs, MOS FETs, PINs, and Varactors, etc., render the SiGe technology a new and exciting paradigm for innovative circuit designs suitable for the realization of “system-on-chip” circuits.
In conventional microwave circuits, switches are commonly implemented using SiGe PIN diodes. However, PIN devices consume DC power and need complex bias supply circuits, both of which negatively impact system efficiency, prime power, size and thereby cost.
Switches implemented using SiGe NMOS devices consume little or no DC power, but are typically limited in bandwidth. For example, prior silicon (Si) based (0.18 um NMOS) RF switching devices offered by the IBM 7-HP process have a maximum useful frequency of less than 5 GHz. Above this frequency, unwanted parasitics associated with the NMOS device become a significant factor in rapidly detracting the switch performance.
Hence, a need exists in the art for an improved microwave switch offering lower power consumption and increased frequency range.